Physicians measured the effectiveness of leech therapy on arthritis pain. (I'm not making this up! See http://www.annals.org/cgi/content/full/139/9/724(Links to an external site.)) They took a sample of 51 patients. They assigned a group of 24 patients to receive "leech therapy," and a control group of 27 patients to receive a conventional pain-relief therapy (diclofenac gel).